@Sarah thank you.. first come basis is an early start right?
Like if you know it's going to be a busy day, get there early to claim your spot. I actually did my first wedding this way. We had the wedding party set up two big tents and the folding chairs basically when the park opened. .
I've done this before and at least in my area you only need to make a reservation if you're using a structure.. if you're just setting up your own stuff in an area it's first come basis.